gistfile1.m

@interface SSLayoutAttributes : UICollectionViewLayoutAttributes
@property (nonatomic, strong) CAGradientLayer *gradient; // a new attribute
@end

@implementation SSLayoutAttributes
- (id) copyWithZone:(NSZone *)zone {

  SSLayoutAttributes *layoutAttribue = [super copyWithZone:zone];
  layoutAttribue.gradient = _gradient;
  return layoutAttribue;
  
}
@end

@interface SSFlowLayout : UICollectionViewFlowLayout
@end
@implementation SSFlowLayout

+(Class) layoutAttributesClass {
  return [SSLayoutAttributes class];
}

- (NSArray*) layoutAttributesForElementsInRect:(CGRect)rect {
  NSArray *array = [super layoutAttributesForElementsInRect:rect];
  for (SSLayoutAttributes *attr in array) {
    if (CGRectIntersectsRect(rect, attr.frame)) {
      [self applyAttributes:attr];
    }
  }
  
  return array;
}

- (UICollectionViewLayoutAttributes*) layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
  SSLayoutAttributes *attr = (SSLayoutAttributes*)[super layoutAttributesForItemAtIndexPath:indexPath];
  [self applyAttributes:(SSLayoutAttributes*)attr];
  return attr;
}

- (void) applyAttributes:(SSLayoutAttributes *)attributes {
  CAGradientLayer *gradient = [CAGradientLayer layer];
  gradient.frame = (CGRect) {CGPointZero, attributes.frame.size};
  gradient.colors = [NSArray arrayWithObjects:(id)[[UIColor colorWithWhite:1.0f alpha:0.0f] CGColor],
                     (id)[[UIColor colorWithWhite:0.9 alpha:0.3f] CGColor],
                     (id)[[UIColor colorWithWhite:0.7 alpha:0.5f] CGColor],
                     (id)[[UIColor colorWithWhite:0 alpha:0.7f] CGColor],
                     (id)[[UIColor colorWithWhite:0 alpha:0.95f] CGColor], nil];
  attributes.gradient = gradient;
}
@end